Extremely low birth weight (ELBW, <1000 gram) infants experience the highest incidence and case fatality of NEC. Biomarkers to predict NEC are lacking, especially in ELBW infants. Exciting new data indicate that specific fucosylated and sialylated glycans may serve as powerful predictors of NEC: H-2 is a major glycan epitope produced by the fucosyltransferase encoded by the FUT2 (secretor) gene. Sialyl Lewis a (sLe ) is a major glycan produced by the combined catalytic function of transferases encoded by the FUT3 and a2-3 sialyl transferase genes. Expression of these glycans on the surface of the intestinal tract can be evaluated indirectly through gene polymorphisms or through measurement of salivary glycans. Our preliminary data indicate that risk of NEC is 4-fold higher and risk of death in NEC cases is 9-fold higher in infants with low or absent salivary H-2 and high sLea glycan compared to other ELBW infants, and that risk of death with NEC varies 5-fold among ELBW infants in relation to their FUT2 (secretor) genotype. Thus, we propose a unique study of 600 ELBW infants enrolled in NICUs in Cincinnati, OH and Birmingham, AL, to test the hypotheses that FUT2 genotype and salivary glycan epitopes are strong predictors of risk of NEC, that they also function as biomarkers of intestinal bacterial colonization, and that alone or in combination with other biomarkers, they greatly improve our ability to predict risk of NEC in ELBW infants. The specific aims of this proposal are to: 1) Test FUT2 genotype and salivary H-2 and sLe phenotypes as novel biomarkers of subsequent risk of NEC; 2) Examine the pattern of intestinal bacterial colonization in ELBW infants in relation to their glycan genotype and phenotype, antibiotic treatment history, and NEC outcome; and 3) Determine the predictive value of multivariate models that include multiple putative biomarkers for risk of NEC, including gene polymorphisms, salivary glycans, and measures of early inflammation. This study will collect DNA for genetic studies, serial saliva for molecular phenotyping of antigens by EIA, and stool for microbiome analysis. Intestinal bacteria will be quantified through real-time qPCR of 16sDNA, and the comprehensive microbiome will be quantified by microarray analysis of stool samples. Standardized clinical data will be available through the NICHD Neonatal Research Network (NRN) data system augmented by chart review. We anticipate that the results of this study will provide a rich dataset that clarifies the ontogeny of intestinal glycan expression- microbial ecology and its relation to NEC. This project has unique potential to guide translational research to test novel interventions. Further, glycan expression biomarkers could be developed into new tools for monitoring premature infants. Our proposal directly addresses several objectives of the RFA by finding new biomarkers; improving multivariate predictive models by including biomarkers of early inflammation; and advancing understanding of the intestinal ecology of preterm infants.